1. Field of the Invention
The present invention relates to a digital camera and lens unit. More particularly, the present invention relates to a digital camera and lens unit in which degree of freedom in selecting an image sensor can be high.
2. Description Related to the Prior Art
A digital still camera is widely used, and includes a CCD or CMOS image sensor to photograph an object image to create image data of a digital form. In the digital still camera, image data is created by a CCD image sensor, and written to a frame memory as work memory. The image data is processed in image processing of various conditions, for example, Y/C processing of conversion into luminance component data Y and chrominance component data C in image data, distortion eliminating correction for correcting distortion, shading processing for adjusting shading of image, gamma correction, and the like.
JP-U 1-177737 discloses an example of the digital still camera having a camera main unit and a lens unit or lens assembly. The camera main unit includes a signal processor, frame memory and the like. The lens unit includes a photographing lens, image sensor and the like. The lens unit is removably secured to the camera main unit. A plurality of types of the lens unit are prepared as exchange lenses, so a selected one of those can be used in combination with the camera main unit for variety in photographing images.
If the pixel number of the image sensor is high, a data size of image data obtained by the image sensor is also great. A problem may occur if the pixel number of the image sensor is extremely high in comparison with the storage capacity of the frame memory. For example, very long time is required for image processing, or image processing is interrupted. In the lens unit of the known technique, an image sensor must have the number of pixels according to the storage capacity of the frame memory in the camera main unit. Thus, degree of freedom in selecting the image sensor is small or limited.
It is conceivable to incorporate a frame memory of a large storage capacity in the camera main unit. However, the cost of the frame memory will be high. A user who is familiar with popular types of the lens unit will be obliged to use an expensive type, because of the structure distinct from an image sensor with a low number of pixels.